let fun =new Proxy({
  add: function add(val) {
    return val + 100;
  },
  name : 99
}, {
  get: function get(target, key, arg) {
    console.log(target,key, arg);
    return target[key]
  },
  set:function(target,key,value,arg){
    return target[key]=value;
  }
});

console.log(fun.name)
fun.name = 77
console.log(fun.name)